In some types of vault doors, the handle which is used to move the bolt between the latched and unlatched conditions is connected at all times to the bolt means and the locking means. When such doors are in the secured condition, the handle is not movable until after a correct combination is dialed into a lock. A problem with this arrangement is that the mechanical connection between the handle and the lock enables an experienced safe cracker to use the handle to "feel" the lock and decipher its combination.
A number of security devices have been developed which can be used to selectively disengage a handle depending on the condition of a lock. U.S. Pat. Nos. 1,645,917; 1,560,509; 1,560,508; 1,560,504; and 1,560,503 all disclose handles which selectively engage and disengage depending on the condition of a lock. Such devices are not suitable for use with secure doors such as vault doors because the locks are integral with the externally mounted handles. This arrangement causes the entire locking mechanism to be exposed to tampering.
Mechanisms for selectively engaging the handle of a safe door mounted internal to the door are disclosed in U.S. Pat. Nos. 102,780 and 269,953. Such mechanisms suffer the disadvantage that there is mechanical contact at all times between the locking means and the handles which enables a safe cracker to "feel" the locking means. In addition, these mechanisms suffer from the disadvantage that removal of the handle shafts by an attacker will allow the mechanisms to be readily defeated.
Thus, there exists a need for a mechanism that selectively engages and disengages an external handle and the bolt of a vault door in response to the condition of locking means and which mechanically isolates the bolt and locking means from the handle when the door is in the secured condition. Further, there exists a need for a mechanism which cannot be defeated by attack on the shaft to which the external handle is mounted.